Computer users employ writable and rewritable optical discs for a variety of different purposes. They may save programs or data to the discs, for archival or distribution purposes. In the case of CD-type discs, users may make music CD's that can be played in audio CD players, or save music data files to the CD's, such as MP3 files, that can be played in special-purpose CD players. In the case of DVD-type discs, users have greater storage capacity available to them than with CD-type discs, and may be able to make video DVD's that can be played in stand-alone DVD players.
Many types of optical discs include a data side and a label side. The data side is where the data is written to, whereas the label side allows the user to label the optical disc. Unfortunately, labeling can be an unprofessional, laborious, and/or expensive process. Markers can be used to write on optical discs, but the results are decidedly unprofessional looking. Special pre-cut labels that can be printed on with inkjet or other types of printers can also be used, but this is a laborious process: the labels must be carefully aligned on the discs, and so on. Special-purpose printers that print directly on the discs may be used, but such printers are fairly expensive. In the patent application entitled “Integrated CD/DVD Recording and Label”, filed on Oct. 11, 2001, and assigned Ser. No. 09/976,877, a solution to these difficulties is described, in which a laser is used to label optical discs.
When reading or writing from the label or data side of an optical disc, the surface of the optical disc may be presumed to be perfectly flat. However, in actuality, the optical disc surface is typically slightly warped, having a surface topology that can be generally likened to that of a potato chip, albeit with considerably less warping as compared to a potato chip. Although this slightly warped nature of the optical disc surface may be difficult if not impossible to discern with the naked eye, it can affect reading and writing label markings and data on the surface. Performance in reading and writing may be reduced, and quality may be impaired.